An integrated circuit generally contains a multiplicity of circuit components with different operating voltages. For this purpose, the integrated circuit contains voltage generator circuits, for example, voltage stabilization circuits or charge pumps, which can be used to derive internal operating voltages from an externally applied supply voltage. The internal voltage potentials provided by the generator circuits are significant to correct functioning of the circuit components of the integrated circuit. In particular, the magnitude of the internal voltages is crucial for proper operation of the integrated circuit components.
In the case of an integrated semiconductor memory, for example, a DRAM (=dynamic random access memory) semiconductor memory, the memory cells contain a storage capacitor, which can be conductively conducted to a bit line via a selection transistor. If an item of information is intended to be stored in the memory cells, then the selection transistor of the relevant memory cell is turned on, so that the storage capacitor is connected to the connected bit line at low impedance. If the item of information to be stored is a logic 1 information item, then the storage capacitor is charged to a voltage potential of 1.5 V, for example. In order that the logic 1 information item can be stored correctly in the memory cell, it must be ensured that a circuit component provided for this in the integrated circuit provides the stable voltage of 1.5 V corresponding to the logic 1 information item.
Therefore, there is great interest in measuring such internal voltage potentials both at the wafer level and at the component level, i.e., at the finished device. At the wafer level, there is either the possibility of replacing a defective internal voltage generator circuit by an intact circuit, or saving production costs by not constructing the damaged integrated circuit any further. At the component level, the measurement of internal voltage potentials of an integrated circuit makes it possible to ensure that only functional devices are supplied. Furthermore, there is the possibility of demarcating the cause of failure of a defective device in relation to the functioning of internal generator circuits.
In order to measure internal voltages at the wafer level, special metallic areas have been provided in the layout, via which metallic areas probes of a measurement system can measure internal voltages. However, viable chip area has been taken up in order to provide enough space for the probes of the measurement systems. Likewise, the layout of an integrated circuit has often not been able to be designed optimally in terms of circuitry due to the additional interconnects and terminal pads. Finally, with regard to the test systems used, a complex hardware has often been required in order, for example, to position the probes onto the metallic terminal areas provided therefore in the integrated circuit.
An integrated circuit, which can be used to determine internal voltage potentials without the use of expensive measurement systems at the wafer level and at the component level, and a method, which can be used to determine internally generated voltage potentials of an integrated circuit are desirable.